High density cobalt-manganese coprecipitated nickel hydroxide and process for its production

ABSTRACT

The present invention provides high density cobalt-manganese coprecipitated nickel hydroxide, particularly having a tapping density of 1.5 g/cc or greater, and a process for its production characterized by continuous supply of an aqueous solution of a nickel salt which contains a cobalt salt and a manganese salt, of a complexing agent and of an alkali metal hydroxide, into a reactor either in an inert gas atmosphere or in the presence of a reducing agent, continuous crystal growth and continuous removal.

FIELD OF THE INVENTION

[0001] The present invention relates to high density cobalt-manganesecoprecipitated nickel hydroxide with excellent charge/discharge cycleproperties and high temperature stability, which is suitable as apositive electrode active material for a lithium ion secondary battery,and to a process for its production.

BACKGROUND OF THE INVENTION

[0002] Recently, attempts have been made to add other components tonickel hydroxide used as the starting material for production of lithiumnickel oxide, for the purpose of including additional components withlithium nickel oxide for use as the positive electrode active materialof lithium ion secondary batteries in order to improve theircharge/discharge cycle properties and high temperature stability (JP-A10-316431).

[0003] However, with the conventional process it has been difficult toobtain nickel hydroxide particles containing cobalt and manganese as theadditional components while still maintaining density sufficient forcurrent requirements.

[0004] The above-mentioned conventional production process givesparticles that are inadequate for use in the positive electrode of alithium ion secondary battery, and thus it has become an important goalto develop high density nickel hydroxide with a high cobalt andmanganese content that exhibits a stable high utilization rate at hightemperatures and low cycle deterioration.

SUMMARY OF THE INVENTION

[0005] As a result of diligent research directed toward achieving thisgoal, the present inventors have completed the present invention uponfinding that it is possible to obtain high density cobalt-manganesecoprecipitated nickel hydroxide by continuously supplying a complexingagent and an alkali metal hydroxide to an aqueous solution of a nickelsalt containing a cobalt salt and a manganese salt while adequatelystirring in an aqueous solution either in an inert gas atmosphere or inthe presence of an appropriate reducing agent, and accomplishingcontinuous crystal growth and continuous removal.

[0006] In other words, the present invention relates to high densitycobalt-manganese coprecipitated nickel hydroxide with a tapping densityof 1.5 g/cc or greater.

[0007] The invention further relates to high density cobalt-manganesecoprecipitated nickel hydroxide characterized in that, where thecobalt-manganese coprecipitated nickel hydroxide is represented as(Ni_((1-x-y))Co_(x)Mn_(y))(OH)₂, 1/10≦x≦1/3 and 1/20≦y≦1/3.

[0008] The invention still further relates to a process for productionof high density cobalt-manganese coprecipitated nickel hydroxide,characterized by continuous supply of an aqueous solution of a nickelsalt which contains a cobalt salt and a manganese salt, of a complexingagent and of an alkali metal hydroxide, into a reactor either in aninert gas atmosphere or in the presence of a reducing agent, continuouscrystal growth and continuous removal. It particularly relates to thisprocess wherein the reducing agent is hydrazine.

[0009] The invention also includes Li(Ni_((1-x-y))Co_(x)Mn_(y))O₂obtained by calcining a cobalt-manganese coprecipitated nickel hydroxideaccording to the invention with an appropriate lithium salt.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is an electron micrograph of high density cobalt-manganesecoprecipitated nickel hydroxide according to the invention.

DETAILED DESCRIPTION OF THE INVENTION High Density Cobalt-manganeseCoprecipitated Nickel Hydroxide

[0011] The cobalt-manganese coprecipitated nickel hydroxide of theinvention is characterized by having high density, and specifically, adensity of 1.5 g/cc or greater. The specific surface area of thecobalt-manganese coprecipitated nickel hydroxide of the invention is inthe range of 8-20 m²/g, and as shown in FIG. 1 it is spherical with amean particle size in the range of 5-20 μm.

[0012] Although the content of the cobalt and manganese as additionalcomponents is not particularly restricted, if represented by(Ni_((1-x-y))Co_(x)Mn_(y))(OH)₂ the ranges are preferably 1/10≦x≦1/3 and1/20≦y≦1/3.

Production Process

[0013] The production process for the cobalt-manganese coprecipitatednickel hydroxide of the invention accomplishes production of nickelhydroxide with high density of coprecipitated cobalt and manganese bycontinuous supply of an aqueous solution of a nickel salt containing acobalt salt (cobalt (II) ion) and a manganese salt (manganese (II) ion),of a complexing agent and of an alkali metal hydroxide, to a reactorwith adequate stirring either in an inert gas atmosphere or in thepresence of a reducing agent, continuous crystal growth and continuousremoval of the resulting precipitate.

[0014] Here, the salt concentration, complexing agent concentration, pHand temperature in the reactor are kept within a fixed range tosatisfactorily control the powder properties, such as the crystallinity,tapping density, specific surface area, particle size, etc.

[0015] Specifically, there is obtained high density cobalt-manganesecoprecipitated nickel hydroxide wherein, as represented by(Ni_((1-x-y))Co_(x)Mn_(y))(OH)₂, 1/10≦x≦1/3 and 1/20≦y≦1/3, the tappingdensity is 1.5 g/cc or greater, the specific surface area is 8-30 m²/gand the mean particle size is 5-20 μm.

[0016] For the high density cobalt-manganese coprecipitated nickelhydroxide, the salt concentration in the vessel is preferably kept inthe range of 50-200 mS/cm ±5 mS/cm and the ammonium ion concentration ispreferably kept in the range of 1-10 g/L ±0.5 g/L. The reaction pH ispreferably kept in the range of 11.0-13.0 ±0.05, and the reactiontemperature is preferably kept in the range of 25-80° C. ±0.5° C.

[0017] As salt concentration adjustors there may be mentioned sodiumchloride, potassium chloride, sodium sulfate, potassium sulfate,ammonium chlorate, ammonium sulfate and the like. As calcium salts theremay be used nitrate, acetate or oxalate salts.

[0018] The production process of the invention is based on the highdensity nickel hydroxide production process described in JP-A 10-97856but is characterized by further adding an appropriate reducing agent.That is, while adequate stirring is usually necessary, this results ininclusion of air, etc. which causes partial oxidation of the unstablecobalt (II) ion or manganese (II) ion and prevents a product withsufficient density from being obtained. In order to control suchoxidation, the production process is carried out either in an inert gasatmosphere or in the presence of a reducing agent. The added reducingagent is not particularly restricted, but hydrazine is preferred.

[0019] In most cases when precipitating solid crystals from aqueoussolution, a high concentration gradient results in abundantprecipitation of fine particles. That is, the mechanism by which solidcrystals precipitate from aqueous solution involves the aqueous solutionpassing from presaturation→saturation→supersaturation→crystalprecipitation. Growth of crystals requires this mechanism to be effectedas slowly as possible, and a low concentration gradient near saturationis necessary for this purpose. Nevertheless, the solubility curves forhydroxides of nickel, cobalt and manganese vary considerably accordingto the pH. In other words, the metal ion concentration gradient is verylarge with respect to the pH. Only production of fine particlestherefore can be expected by ordinary methods. According to theinvention, however, the metal ions are in a complex salt with ammoniumso that the concentration gradient of the metal ions with respect to thepH is reduced in aqueous solution to achieve growth of particles.

[0020] With pH control alone, decomposition and evaporation of ammoniaalters the ammonium ion concentration in the solution, such thatgeneration of crystal nuclei produced from the ammonium complex saltbecomes unstable. Only by controlling the ammonium ion concentration ofthe solution does generation of crystal nuclei become constant, so thatuniform growth of particles occurs. In order to maintain such amechanism, the ammonium ion source and alkali metal hydroxide mustconsistently match the necessary amount of metal ion, and therefore thereaction process is preferably carried out in a continuous manner. Byspeeding up the stirring rate, an abrading effect also occurs betweenthe particles, and this repeated abrasion and growth result influidized, spherical high density particles.

[0021] The ammonium ion source for the reaction as a complexing agentaccording to the invention is used as a reaction intermediate, asrepresented by reaction formulas (1) and (2). Here, the nickel salt,ammonium ion source and alkali metal hydroxide are nickel sulfate,ammonia and sodium hydroxide, respectively. (Cobalt and manganese areomitted in order to simplify the formulas, but they likewise progressthrough ammonium complex salts.) As is apparent from the formulas, 4equivalents of ammonia are not necessary, as about 0.5 equivalent atmost is sufficient.

NiSO₄+4NH₃+2NaOH→Ni(NH₃)₄(OH)₂+Na₂SO₄  (1)

Ni(NH₃)₄(OH)₂→Ni(OH)₂+4NH₃  (2)

EXAMPLE 1

[0022] After placing 450 L of water in a 500 L cylindrical reactorequipped with an overflow pipe and a stirrer provided with two 250φpropeller type stirring blades, a 30% sodium hydroxide solution wasadded to a pH of 12.6 and the temperature was kept at 50° C. whilestirring at a speed of 320 rpm.

[0023] Next there were simultaneously added to the reactor in acontinuous manner a solution containing a mixture of 1.7 mol/L nickelsulfate solution, 1.5 mol/L cobalt sulfate solution and 1.1 mol/Lmanganese sulfate aqueous solution in a volume ratio of 35:20:9 at aflow rate of 200 cc/min, a 6 mol/L ammonium sulfate solution at 63cc/min and a 1 wt % hydrazine aqueous solution at 10 cc/min.

[0024] Also, 30% sodium hydroxide was intermittently added until thesolution in the reactor reached a pH of 12.6, to form cobalt-manganesecoprecipitated nickel hydroxide particles.

[0025] After 120 hours when the reactor reached a steady state, thecobalt-manganese coprecipitated nickel hydroxide particles werecontinuously removed for 24 hours from the overflow pipe and washed,filtered and dried at 100° C. for 15 hours to obtain cobalt-manganesecoprecipitated nickel hydroxide dry powder with a component ratio ofNi:Co:Mn=60:30:10.

[0026] The tapping density of the obtained cobalt-manganesecoprecipitated nickel hydroxide powder was measured in the mannerdescribed below.

[0027] Sample preparation: The cobalt-manganese coprecipitated nickelhydroxide powder obtained above was used in the manner described below.

[0028] The mass [A] of a 20 mL cell [C] was measured, and the crystalswere allowed to naturally fall into the cell through a 48 mesh filter tofill it. The mass [B] and filling volume [D] of the cell were measuredafter tapping 200 times using a “TAP DENSER KYT-3000” by SeishinEnterprise Co., Ltd. with a mounted 4 cm spacer. The following equationswere used for calculation.

[0029] Tapping density=(B−A)/D g/ml

[0030] Bulk density=(B−A)/C g/ml

[0031] Measurement results: Tapping density=1.91 g/cc

EXAMPLE 2

[0032] Cobalt-manganese coprecipitated nickel hydroxide with a componentratio of Ni:Co:Mn=50:30:20 was produced and the tapping density thereofmeasured under the same conditions as Example 1, except that the nickelsulfate solution, cobalt sulfate solution and manganese sulfate solutionwere mixed in a volume ratio of 30:20:18 and the pH of the reactionsolution used to form the cobalt-manganese coprecipitated nickelhydroxide particles was 12.4. The tapping density was 1.71 g/cc.

EXAMPLE 3

[0033] After placing 13 L of water in a 15 L cylindrical reactorequipped with an overflow pipe and a stirrer provided with one 70φpaddle type stirring blade, a 30% sodium hydroxide solution was added toa pH of 10.9 and the temperature was kept at 50° C. while stirring at aspeed of 1000 rpm. Nitrogen gas was also continuously supplied to thereactor at a flow rate of 0.5 L/min, and the atmosphere in the reactorwas replaced with a nitrogen atmosphere. Next there were simultaneouslyadded to the reactor in a continuous manner a solution containing amixture of 1.7 mol/L nickel sulfate solution, 1.5 mol/L cobalt sulfatesolution and 1.1 mol/L manganese sulfate aqueous solution in a volumeratio of Ni:Co:Mn=1:1:1 (molar ratio) at a flow rate of 12 cc/min and a6 mol/L ammonium sulfate solution at 1.2 cc/min. Also, 30% sodiumhydroxide was intermittently added until the solution in the reactorreached a pH of 10.9, to form cobalt-manganese coprecipitated nickelhydroxide particles. After 120 hours when the reactor reached a steadystate, the cobalt-manganese coprecipitated nickel hydroxide particleswere continuously removed for 24 hours from the overflow pipe andwashed, filtered and dried at 100° C. for 15 hours to obtaincobalt-manganese coprecipitated nickel hydroxide dry powder with acomponent ratio of Ni:Co:Mn=1:1:1. The tapping density was 1.82 g/cc.

COMPARATIVE EXAMPLE 1

[0034] After placing 450 L of water in a 500 L cylindrical reactorequipped with an overflow pipe and a stirrer provided with one 250φpropeller type stirring blade, a 30% sodium hydroxide solution was addedto a pH of 12.6 and the temperature was kept at 50° C. while stirring ata speed of 350 rpm. Next there were simultaneously added to the reactorin a continuous manner a solution containing a mixture of 1.7 mol/Lnickel sulfate solution, 1.5 mol/L cobalt sulfate solution and 1.1 mol/Lmanganese sulfate aqueous solution in a volume ratio of 35:20:9 at aflow rate of 200 cc/min and a 6 mol/L ammonium sulfate solution at 63cc/min. Also, 30% sodium hydroxide was intermittently added until thesolution in the reactor reached a pH of 12.6, to form cobalt-manganesecoprecipitated nickel hydroxide particles. After 120 hours when thereactor reached a steady state, the cobalt-manganese coprecipitatednickel hydroxide particles were continuously removed for 24 hours fromthe overflow pipe and washed, filtered and dried at 100° C. for 15 hoursto obtain cobalt-manganese coprecipitated nickel hydroxide dry powderwith a component ratio of Ni:Co:Mn=60:30:10. The tapping density was1.40 g/cc.

COMPARATIVE EXAMPLE 2

[0035] Cobalt-manganese coprecipitated nickel hydroxide with a componentratio of Ni:Co:Mn=50:30:20 was produced and the tapping density thereofmeasured under the same conditions as Comparative Example 1, except thatthe nickel sulfate solution, cobalt sulfate solution and manganesesulfate solution were mixed in a volume ratio of 30:20:18 and the pH ofthe reaction solution used to form the cobalt-manganese coprecipitatednickel hydroxide particles was 12.4. The tapping density was 1.33 g/cc.

EFFECT OF THE INVENTION

[0036] According to the present invention it is possible to obtain highdensity cobalt-manganese coprecipitated nickel hydroxide having highdensity, and particularly a tapping density of 1.5 g/cc or greater, bycontinuous supply of an aqueous solution of a nickel salt which containsa cobalt salt and a manganese salt, of a complexing agent and of analkali metal hydroxide, into a reactor either in an inert gas atmosphereor in the presence of a reducing agent, continuous crystal growth andcontinuous removal.

What is claimed is:
 1. High density cobalt-manganese coprecipitatednickel hydroxide with a tapping density of 1.5 g/cc or greater.
 2. Highdensity cobalt-manganese coprecipitated nickel hydroxide according toclaim 1, characterized in that, where said cobalt-manganesecoprecipitated nickel hydroxide is represented as(Ni_((1-x-y))Co_(x)Mn_(y))(OH)₂, 1/10≦x≦1/3 and 1/20≦y≦1/3.
 3. A processfor production of high density cobalt-manganese coprecipitated nickelhydroxide of claim 1, characterized by continuous supply of an aqueoussolution of a nickel salt which contains a cobalt salt and a manganesesalt, of a complexing agent and of an alkali metal hydroxide, into areactor either in an inert gas atmosphere or in the presence of areducing agent, continuous crystal growth and continuous removal.
 4. Theprocess of claim 3 wherein said reducing agent is hydrazine.